Mechanical ventilatory support is the accepted technique for providing respiratory function in critically ill patients. Conventional mechanical ventilation (CMV) reproduces physiologic tidal volumes and respiratory rates and is used commonly in a large number of patients requiring ventilatory support. However, there are patients who either do not respond to CMV or who are not in settings where conventional support can be cimplemented. In addition, complications related to the relatively high airway pressures required for CMV (baro-trauma) can limit its effective use. Recent investigation into high frequency jet ventilation (HFJV) has demonstrated a new technique that could be adpated to use for patients who require ventilatory assistance, but who cannot be supported on CMV. High frequency jet ventilation has been successfully used as a ventilatory support device in animal in-vivo experiment and human clinical settings and has demonstrated the ability to provide acceptable aveolar ventilation at airway pressures below that needed for equivalent CMV. Although HFJV has not been accepted as a universal technique it has several attractive features that could justify its use in emergency airway management settings as are found by ambulance technicians and paramedics. Particularly attractive is the fact that HFJV can be implemented by para-medical personnel by performing a percutaneous tracheal airway access with a small bore catheter. If such a rapid, effective emergency airway control method were available, it could significantly improve the survival of cardio-pulmonary resuscitations performed in the community at large by ambulance personnel. Existing HFJV hardware has been large in size and relatively costly and not readily adpated to portability and use by field personnel. If a portable, reliable system could be developed it would could make available a HFJV system that could be used by a large number of personnel in resuscitations that occur in the community at large. This program proposes to develop a pneumatically powered, fluidically controlled high frequency jet ventilator that could be adapted toportable use by para-medical and ambulance personnel in the field.